1. Field of the Invention
The present invention relates to an ejector used for a fuel cell system including a fuel cell.
2. Description of the Related Art
Recently, there have been many developments regarding a fuel cell vehicle having a fuel cell such as a polymer electrolyte fuel cell (PEFC). In such a fuel cell vehicle, a motor is rotated by power generated by the fuel cell so as to drive the vehicle.
In general, the fuel cell includes stacks of a plurality of single cells. Each single cell includes MEA (membrane electrode assembly). When fuel gas (hydrogen) is supplied for an anode of the MEA, and oxidant gas (air including oxygen) is supplied for a cathode thereof, difference in potential is caused on each single cell, which is electrically connected to an outer load such as a motor, and then the fuel cell starts generating power.
There has been proposed a fuel cell system including a fuel cell, in which fuel off-gas (hydrogen off-gas) discharged from the fuel cell is mixed with a new fuel gas (hydrogen) to be supplied for the fuel cell, so as to be re-circulated, thereby to utilize the fuel gas as well as to enhance energy efficiency of the PEFC. In such a case of a prior art, there has been known a fuel cell system that re-circulates fuel off-gas using an ejector.
By the way, it has been pointed out that because, in such a fuel cell system using an ejector, each diameter of a nozzle and a diffuser that are included in the ejector is fixed, it is difficult to supply fuel gas for the fuel cell in accordance with various driving situations (e.g. various driving situations through an idling driving to a high speed driving) of a fuel cell vehicle including the fuel cell system.
In the light of this problem, JP2004-178843A discloses a fluid supply apparatus for a fuel cell whose first to third ejectors have each nozzle with a different diameter, and whose first and second switch valves switch a fuel supply passage of fuel gas for one of the first to third ejectors; and by using combination of on-off operations of the first and the second switch valves, fuel gas is supplied for a desired one selected from the first to third ejectors.
However, such a fluid supply apparatus for a fuel cell disclosed in JP2004-178843A has the three ejectors having each nozzle with a different diameter and the two switch valves of electromagnetic valves that switch the fuel gas supple passage for the ejectors within a unit body of the apparatus; therefore, the size of the overall apparatus inevitably becomes larger, so that there has been desired to reduce a size and weight of an overall fluid supply apparatus.
It has also been desired to stabilize discharge rate of fuel gas discharged from a nozzle of an ejector, and to supply fuel gas at a stable flow rate for a fuel cell.
In addition, in the above fluid supply apparatus for a fuel cell, the first and second switch valves are electromagnetic valves having each solenoid, so that when a movable core attracted to a fixed core due to excitation of the solenoids, or when the movable core returns to its original position when the solenoid becomes unexcited, the movable core collides against the fixed core of magnetic material or other metal members and may generate collision noises and vibrations. Hence, there has been desired to prevent such collision noises and vibrations of the solenoid from propagating to a vehicle interior, so as to ensure quietness in the vehicle interior.
Yet, in the above fluid supply apparatus for a fuel cell, the first and the second switch valves are electromagnetic valves of solenoids each including a movable core and a fixed core, and the valves are vertically-installed type in which each movable core slides in the vertical direction thereby to displace its valve body. If an electromagnetic valve with a horizontally-installed solenoid is employed in order to reduce a vertical size of the overall ejector apparatus, when a movable core is attracted to a fixed core in the horizontal direction due to excitation of the solenoids, or when the movable core returns in the horizontal direction to its original position when the solenoid becomes unexcited, the axis of the movable core becomes deviated in the vertical direction due to its own weight in a clearance around the sliding part thereof so that friction against other members becomes greater, which may cause a problem of deterioration of the movable core duration.